Boron phosphide (BP) is conventionally known as one of Group III-V compound semiconductors (see, Iwao Teramoto, Handotai Device Gairon (Introduction to Semiconductor Devices), page 28, Baifukan (Mar. 30, 1995)). The boron phosphide is an almost covalent bonding semiconductor having a Phillips ionicity (=δ) as small as 0.006 (see, Phillips, Handotai Ketsugo Ron (Bonds and Bands in Semiconductors), 3rd imp., page 51, Yoshioka Shoten (Jul. 25, 1985)). Furthermore, the boron phosphide is a zinc-blend type cubic crystal (see, Handotai Device Gairon (Introduction of Semiconductor Device), supra, page 28) and therefore, degenerated in the valence band unlike hexagonal wurtzite-type semiconductor crystals such as gallium nitride (GaN) (see, Toshiaki Ikoma and Hideaki Ikoma, Kagobutsu Handotai no Kiso Bussei Nyumon (Guide for Basic Physical Properties of Compound Semiconductor), 1st ed., pp. 14–17, Baifukan (Sep. 10, 1991)). Accordingly, boron phosphide is fundamentally facilitated in the formation of a p-type electrically conducting layer as compared with, for example, wurtzite crystal-type GaN having a high ionicity (δ) of 0.500 (see, Handotai Ketsugo Ron (Bonds and Bands in Semiconductors), supra, page 51).
A p-type boron phosphide semiconductor layer is conventionally utilized, for example, as a contact layer for providing an electrode in a laser diode (LD) (see, JP-A-10-242567 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). There are also known techniques of fabricating LDs or light-emitting diodes (LEDs) from a stacked layer structure having a p-type boron phosphide layer as a buffer layer on a gallium arsenide (GaP), silicon carbide (SiC) or GaN single crystal substrate. In another conventional light-emitting device, a mixed crystal of boron phosphide and aluminum gallium nitride (AlxGa1−xN: 0≦X≦1), where a p-type impurity is added, is used as a light-emitting layer (see, JP-A-2-275682). In conventional techniques, the p-type boron phosphide layer is formed by a metal organic chemical vapor deposition (MOCVD) method using magnesium (Mg) or zinc (Zn) as the p-type impurity (see U.S. Pat. No. 6,069,021).
However, it is pointed out that in so-called undoped boron phosphide where an impurity is not intentionally added, phosphorus occupying the vacancy of boron may be present (see, Katsufusa Shono, Cho LSI Jidai no Handotai Gijutsu 100 Shu (100 Collections of Semiconductor Technique in VLSI Generation) [III], Ohmu Sha (Apr. 1, 1982), Electronics Library 18, pp. 86–87, appendix of “Denshi Zasshi Electronics (Electric Journal Electronics)”, Vol. 27, No. 4 (April, 1982)). On the contrary, the possibility of the presence of boron occupying the vacancy of phosphorus is suggested (see, (Cho LSI Jidai No Handotai Gijutsu (Semiconductor Technique in VLSI Generation) [III], supra, pp. 86–87). In other words, there is suggested the possibility that a phosphorus atom occupying the normal lattice site of boron is present. Also, the possibility of the presence of boron occupying the vacancy of phosphorus is suggested. Phosphorus occupying the normal lattice site of zinc-blende type cubic boron phosphide is considered to act as a donor (see, Cho LSI Jidai No Handotai Gijutsu (Semiconductor Technique in VLSI Time) [III]), supra, pp. 86–87). On the other hand, boron occupying the normal lattice site of phosphorus is considered to act as an acceptor (see, Cho LSI Jidai No Handotai Gijutsu (Semiconductor Technique in the VLSI Age) [III]), supra, pp. 86–87).
As described above, the possibility that the boron phosphide layer contains anti-site is suggested (see, Hideaki Ikoma and Toshiaki Ikoma, Kagobutsu Handotai no Kiso Bussei Nyumon (Guide for Basic Physical Properties of Compound Semiconductor), 1st ed., page 141, Baifukan (Sep. 10, 1991)). The anti-site defect is a defect involving the constituent elements boron (B) and phosphorus (P) and therefore, is present in a large amount. For example, in the state in which phosphorus occupying the vacant lattice point of boron, which is considered to act as a donor, is present in a large amount, even if a p-type impurity is doped, a BP layer showing p-type conduction is not always stably obtained. More specifically, unlike conventional group III-V compound semiconductors having a large ionicity, such as gallium arsenide (GaAs: δ=0.310) and gallium nitride (GaN: δ=0.500), a controlled p-type or n-type boron phosphide-based semiconductor layer, for example, having a small resistivity cannot be stably obtained only by the simple addition of a p-type or n-type impurity.
Moreover, the effect given by the addition of a p-type or n-type impurity on, for example, production of boron vacancy is not yet clarified. Therefore, a p-type or n-type impurity capable of suppressing the change in the concentration of anti-site defects and suitable for stably obtaining a p-type or n-type boron phosphide-based semiconductor layer having a desired resistivity has not been proposed. The present invention has been made to solve the above-described problems of conventional techniques and the object of the present invention is to provide technical means where, in a Group III-V compound semiconductor having a low ionicity and a strong covalent bonding property, particularly in obtaining an n-type or p-type boron phosphide-based semiconductor layer, an n-type or p-type boron phosphide-based semiconductor layer having, for example, precisely controlled carrier concentration can be stably obtained by adding an n-type or p-type impurity while taking account of the relative concentration of anti-site defects. Another object of the present invention is to provide a boron phosphide-based semiconductor device such as a light-emitting device, fabricated by utilizing an n-type or p-type boron phosphide-based semiconductor layer having a desired resistance.